A typical system such as a computer or a game device comprises a ROM storing therein software that is executed at power on (hereinafter, this software will be referred to as “boot code”). This ROM has a bus width narrower than a bus width of a central processing unit (CPU), and has an access speed which is also low. Therefore, in many systems, the boot code is executed after having been transferred to a random access memory (RAM) which is capable of high-speed access.
Specifically, referring to FIG. 3, immediately after power on, a CPU 20 jumps to an address of a flash ROM 26 mounted on a motherboard to execute the contents of the flash ROM 26. Then, the CPU 20 transfers a boot code from the flash ROM 26 to a main memory 24 and executes the boot code on the main memory 24. Through the execution of the boot code, various controllers, secondary storage devices (floppy disk drive, hard disk drive (HDD), CD-ROM drive, etc.), and other devices are initialized, and an operating system is transferred to the main memory 24. The flash ROM 26 has a function of retaining internal data even when the power is turned off, and therefore in a conventional system is an essential component for starting up the system.
On the other hand, in order to achieve reduction in cost of the product, it is often desirable to decrease the number of components. This approach has been employed also in personal computers and game devices. Techniques have been proposed in Japanese patent publications JP-A-H11-143718 and JP-A-2000-112762, which aim to achieve reduction in cost of the product by eliminating the flash ROM 26 storing the boot code.
In the technique described in JP-A-H11-143718, a dedicated flash ROM for storing a basic input/output system (BIOS) (equivalent to “boot code” in the present invention) is not used, which simplifies the configuration of a small-sized computer, thus achieving reduction in cost. The BIOS is instead stored in a predetermined area of an HDD, and an HDD controller maps the BIOS stored in the HDD onto a RAM under the control of a memory controller. The BIOS is executed on the RAM after the BIOS stored in the HDD has been transferred to the RAM under the control of the memory controller. This means that the memory controller is provided with a memory storing a program for transfer of the BIOS, and an arithmetic unit. This causes the memory controller to carry out processing apart from ordinary processing. Consequently, inasmuch as a memory controller having high processing capability is required, the cost of the memory controller is increased, which offsets the reduction in cost obtained by eliminating the flash ROM.
In the technique of JP-A-2000-112762, a system BIOS is stored in a dedicated storage area of an HDD, and a mechanism is provided for reading and executing the system BIOS upon system startup, thereby eliminating a flash ROM for storing the system BIOS. A microcomputer provided inside the HDD serves as the mechanism for reading and executing the BIOS upon system startup. In this approach the added cost of providing the microcomputer offsets the cost reduction from eliminating the flash ROM.